Certain N-substituted halopyrrolidones are known to be useful as herbicides of general application. Such compounds and their utility are disclosed in commonly assigned copending applications Ser. No. 647,962, filed Jan. 9, 1976, and Ser. No. 647,963, filed Jan. 9, 1976. These compounds in general have the following formula ##STR3## in which X is selected from the group consisting of hydrogen, chlorine, and methyl;
Y is selected from the group consisting of hydrogen, chlorine, and bromine; PA1 Z is selected from the group consisting of chlorine and bromine; PA1 R.sup.1 is selected from the group consisting of hydrogen and C.sub.1 -C.sub.4 alkyl; and PA1 R.sup.2 is selected from the group consisting of C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.6 alkenyl, C.sub.1 -C.sub.6 haloalkyl, C.sub.3 -C.sub.7 cycloalkyl, C.sub.4 -C.sub.8 cycloalkylalkyl, benzyl, chlorobenzyl, and ##STR4## in which R.sup.3 is selected from the group consisting of hydrogen, C.sub.1 -C.sub.4 alkyl, acetyl, chlorine, bromine, fluorine, iodine, trifluoromethyl, nitro, cyano, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulfinyl, C.sub.1 -C.sub.4 alkylsulfonyl, trifluoromethylthio, trifluoromethylsulfinyl, trifluoromethylsulfonyl, pentafluoropropionamido, and 3-methylureido; and R.sup.4 is selected from the group consisting of hydrogen, C.sub.1 -C.sub.4 alkyl, chlorine, and trifluoromethyl. PA1 aliphatic compounds, for example heptane or octane; PA1 aromatic compounds, for example toluene, xylene, or mesitylene; PA1 chlorinated aliphatic or aromatic compounds, for example, 1,2-dichloroethane or chlorobenzene; PA1 ethers, for example 1,2-dimethoxyethane, diethyl ether, tetrahydrofuran, or 1,4-dioxane;
According to the above-mentioned references, the compounds are prepared by the intramolecular cyclization of an .alpha.-halogen-containing N-2-alkenyl amide in the presence of a catalytic amount of ferrous ion.
It has now been discovered that the intramolecular cyclization referred to above can be catalyzed by catalysts other than ferrous ion. It is therefore an object of the present invention to provide a novel process for the preparation of N-substituted halopyrrolidones of formula (I). Other objects of the invention will be evident from the following description.